1. Field of the Invention
This invention relates, in general, to methods and apparatus for determining the composition of skeletal muscle, and more particularly to a method and apparatus for non-invasive in vivo determination of skeletal muscle composition.
2. Description of the Prior Art
Skeletal muscle fiber is commonly classified into two types--Type I and Type II. Type I muscle has a slow contraction time and a low tension output as compared with type II. A high percentage of Type II muscle fiber is therefore a prerequisite for performing fast contractions with high tension outputs. Determination of muscle fiber composition is important for medical as well as physical education reasons in promoting the understanding of muscle building; atrophy; fatigue; soreness; rehabilitation; effect of exercise; athletic potential; effect of diets; and many other factors.
Prior to the present invention, muscle biopsies with histochemical staining has been used to determine fiber composition of various muscles. In the histochemical technique, thin transverse sections of muscle are caused to adhere to glass cover slips. By incubating and rinsing the sections in solutions of specific chemical composition, the fiber cross sections may be preferentially stained according to their type and metabolic characteristics. The staining intensities from histochemcial procedures are assessed qualitatively, using a light microscope. This process, although appearing simple, requires specific equipment; analyzation is very tedious and time-consuming, and requires a technician specialized in histochemical staining procedure. It is, therefore, apparent that assessment of fiber type through histochemical staining is confined to a specialized facility or laboratory. Further, such histochemical determination obviously results in damage to the muscle being studied, because of the biopsy or biopsies. Such damage, with the obvious discomfiture involved, precludes periodic testing and the subject is often loathe to submit to the biopsies. The method is therefore completely unsuitable for frequent use except for serious medical evaluations.
Relevant work in the area of indirect measurement of physiological profile testing and determination include the studies of Thorstensson, Journal of Applied Physiology 40:12-16, 1976, who has showed a correlation between muscle performance and fast-twitch muscle fibers; Gregor, Journal of Applied Physiology 47:388-392, 1979, who found a correlation between fast-twitch area and torque produced; Lower and Castill, Human Performance Laboratory, Ball State University, 1980; and Petrofsky, Medicial and Biological Engineering and Computing, 17:525-533, 1979, and Petrofsky and Lind, American Journal of Physiology 36:185-196, 1979, showing muscle response to stimulation voltage.